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Radiocarbon measurements were performed on gas splits from gas extracted for d13C measurements by the University of Washington group (headed by Dr. Paul Quay). The measurements were done by AMS by NOSAMS (http://www.whoi.edu/nosams/home).

Radiocarbon Measurement Methodology:
Samples were drawn from 30 liter Niskin bottles to 500 ml gas tight bottles and treated with mercuric chloride. The CO2 was stripped from the water using acidification in high vacuum line, a small split was taken for 13C analysis by another laboratory, and the remainder flame sealed in a glass ampoule.

The gas samples were submitted for analysis to the U.S. National Ocean Sciences Accelerator Mass Spectrometry (NOSAMS) Facility in Woods Hole, MA, USA (http:// http://www.whoi.edu/nosams/home). The CO2 was processed by iron-catalyzed hydrogen reduction to filamentous graphite. The graphite was packed into ~1 mg aluminum targets and analyzed by Cs-sputter accelerator mass spectrometry. Either or both of the following AMS systems were used for measurement (it is NOSAMS policy not to divulge which instrument is used for a particular analysis):

This added information will facilitate subsequent analysis and inter comparison of the datasets.

Bottle parameters in the master file were taken from the GT-C_Bottle and ODF_Bottle datasets. Non-bottle parameters, including those from GeoFish tows, Aerosol sampling, and McLane Pumps, were taken from the TN303 Event Log (version 30 Oct 2014). Where applicable, pump information was taken from the PUMP_Nuts_Sals dataset.

A standardized BCO-DMO method (called "join") was then used to merge the missing parameters to each US GEOTRACES dataset, most often by matching on sample_GEOTRC or on some unique combination of other parameters.

If the master parameters were included in the original data file and the values did not differ from the master file, the original data columns were retained and the names of the parameters were changed from the PI-submitted names to the standardized master names. If there were differences between the PI-supplied parameter values and those in the master file, both columns were retained. If the original data submission included all of the master parameters, no additional columns were added, but parameter names were modified to match the naming conventions of the master file.

See the dataset parameters documentation for a description of which parameters were supplied by the PI and which were added via the join method.

An AMS measures "long-lived radionuclides that occur naturally in our environment. AMS uses a particle accelerator in conjunction with ion sources, large magnets, and detectors to separate out interferences and count single atoms in the presence of 1x1015 (a thousand million million) stable atoms, measuring the mass-to-charge ratio of the products of sample molecule disassociation, atom ionization and ion acceleration." AMS permits ultra low-level measurement of compound concentrations and isotope ratios that traditional alpha-spectrometry cannot provide. (more from Purdue University)

PI supplied instrument name: Cs-sputter accelerator mass spectrometry

Dataset-specific description

The CO2 was processed by iron-catalyzed hydrogen reduction to filamentous graphite. The graphite was packed into ~1 mg aluminum targets and analyzed by Cs-sputter accelerator mass spectrometry. Either or both of the following AMS systems were used for measurement: (1) A custom-built compact 500 KV National Electrostatics Corporation (NEC), Middleton, WI model 15SDH-1 accelerator with a 134 position NEC MC-SNICS source. (2) A 2.5 MV US-AMS tandetron accelerator with a modified bouncer-injector and 40 position NEC MC-SNICS source.

A Niskin bottle (a next generation water sampler based on the Nansen bottle) is a cylindrical, non-metallic water collection device with stoppers at both ends. The bottles can be attached individually on a hydrowire or deployed in 12, 24 or 36 bottle Rosette systems mounted on a frame and combined with a CTD. Niskin bottles are used to collect discrete water samples for a range of measurements including pigments, nutrients, plankton, etc.